1. Field of the Invention
The present invention relates to a semiconductor exposure apparatus. More particularly, the present invention relates to a system for detecting the alignment of a reticle and a wafer.
2. Field of the Invention
An exposure apparatus is generally used in manufacturing integrated circuit semiconductor devices to downsize an image on a reticle and transfer the downsized image onto a wafer. However, the reticle and the wafer must be exactly aligned before the exposure process is carried out.
An alignment system is used to check the state of alignment of a reticle and a wafer prior to the exposure process. In such a system, alignment beams emitted from a light source are directed onto an alignment mark of the wafer and are diffracted thereat. The diffracted beams pass through the reticle and through holes 200 (see FIG. 1) of a diaphragm of the system, whereupon they impinge an optical sensor. The beams impinging the optical sensor are analyzed to determine the state of alignment of the reticle and the wafer.
Unfortunately, the conventional alignment system has the following drawbacks. The alignment beams become skewed relative to the optical axis due to long-term use or deterioration of the system. In order to adjust the relative angles or positions of the alignment beams, an operator must disassemble a case of an alignment detecting apparatus and check with his/her naked eye whether the alignment beams are propagating normally with respect to the diaphragm. Therefore, it takes a long time to check the relative angles of the alignment beams. Moreover, the main control system may determine the state of alignment to be satisfactory even when the alignment beams are tilted because there is no reliable means for checking the relative angles of the alignment beams. As a result, the reproducibility of the exposure process is poor.